Referring first to the OHC type valve mechanism that is a typical one of the conventional valve mechanisms, the rotation of a cam 2 causes seesaw movement of a rocker arm 1 around the axis thereof, thereby opening or closing a valve 3, as shown in FIG. 1. In such a valve mechanism, although the wear resistance of the arm 1 which comes into contact with the cam 2 is of importance, the wear resistance of the cam 2 per se is of great importance as well.
As the pad material for the sliding surface of a rocker arm, there is known a high-density material such, as high-speed steel or alloy steel, which is of a structure wherein finely divided carbide is dispersed throughout the martensite matrix, and has a porosity of about 2-3%. The present inventors developed this type of material, for which a Japanese Patent Application No. 55-181916 was filed, said application being now laid-open under No. 57-108245.
Such material, inter alia, an alloy material developed by the present inventors, shows extremely high wear resistance, and serves to reduce the abrasion of the pad. Nonetheless, improvement is required since the improved pad tends to rapidly abraid the associated cam.